Layer 2s (lightning and others that will come), fedimints, and of course their will be centralized financial services bitcoin companies that use bitcoin rails but might have their own private layers on top (I know that's blasphemous to bitcoiners but it will happen).

Maybe sidechains down the road but I think layer 2s and adoption are much more important in the coming years. Focusing on Sidechains now is akin to building a building and working on the gym, pool and sauna on the 50th floor before building the elevator.